Men's relationships with their female friends may be fuelled by an
undercurrent of sexual attraction regardless of whether they are single but
the feeling is not mutual, a new study suggests.

Women are more likely to consider their friendships with men as platonic and only hope that they develop into more if their own relationship is in trouble, researchers found.

Their findings echo the plot of 1989 film When Harry Met Sally, in which Harry, played by Billy Crystal, tells Meg Ryan's character Sally: "Men and women can't be friends because the sex part always gets in the way."

Scientists said the results of the study, reported in the Daily Mail, showed "potential negative consequences" for people in long-term relationships.

Changing social patterns in the spheres of work, higher education and leisure activities have seen friendships between men and women reach unprecedented levels, they said.

But a deeper-lying mating instinct, developed over hundreds of thousands of years of evolution, could make them more complicated than they might seem.

In the study, 88 pairs of young male and female friends were asked to rate their attraction to each other on a secret questionnaire.

Men - whether they were attached or single - were more likely to harbour an attraction to their female friends and want to go out with them than the other way around.

The men also assumed that the women were more sexually interested in them than they actually were - and the women tended not to realise this.

Researchers found that single and attached women had the same level of attraction to their male friends - but attached women only wanted something more if their own relationship was on the rocks. Women were also less attracted to attached men, the study found.

Participants of the study, published in the Journal of Social and Personal Relationships, said benefits gained from friendships with members of the opposite sex included getting good advice and boosting their confidence.

The authors of the research, from the University of Wisconsin, said films and television programmes had helped instill the idea that normal friends could become "friends with benefits" - that is, who have sex with each other.